1. Field of the Invention
The present invention relates generally to lightweight cookware suitable for hiking and camping as well as for food warming trays used in commercial food warming cabinets. More particularly, this invention relates to composite metal cookware which has a very thin layer of stainless steel on the food contacting surfaces with a layer of aluminum bonded thereto. The invention also relates to a method of making the composite metal product used in constructing the lightweight cookware and warming trays.
2. Description of Related Art
Hikers and campers desire lightweight cookware for ease of travel, particularly when backpacking. Such cookware should ideally be strong in order to resist deformation when packed tightly in a backpack, but it should also exhibit high heat conductivity so as to make efficient use of the limited heating fuel carried by the hiker. Such cookware should also offer easy cleaning for the user. Solid aluminum cookware offers light weight in thin sections, but can be easily bent or deformed during hiking due to its relatively weak strength. Cleaning of bare aluminum cook surface is also problematic. A non-stick PTFE surface also lacks long-term durability on aluminum cookware and is prone to abrasive wear. On the other hand, solid stainless steel cookware is strong and offers better cleaning, but is heavy. In addition, stainless steel is very inefficient in thermal conductivity, which results in excessive fuel consumption during cooking, which is a major concern with portable cooking stoves used by hikers.
It is known to produce three-ply composite cookware of stainless steel layers on the cook surface and outer surface with a core layer of aluminum to provide better heat conductivity and strength. However, present techniques for roll bonding stainless steel and aluminum require relatively thick gauges of stainless steel which adversely affects the weight of the cookware, making it unattractive for use in hiking.
Commercial food warming trays, particularly those used in the fast food industry, are typically made from anodized aluminum. These trays each have an electrical resistance heating means affixed to the underside thereof, along with a temperature controlling thermostat, to maintain the food product on the upper surface at a constant desired temperature prior to service. Aluminum is a good material for the warming tray because of its relative light weight and high coefficient of thermal conductivity. In recent times, however, aluminum has fallen into disfavor for use as a food contacting surface in the commercial food preparation industry.
Accordingly, there is a need for replacing aluminum as a food contacting surface in commercial food warming trays. Stainless steel appears to be a potential replacement candidate for aluminum because of its excellent properties concerning chemical inertness toward food, scratch resistance and overall good appearance. Unfortunately, stainless steel has relatively poor thermal conductivity properties compared to aluminum while also being much heavier.
A bimetal composite of stainless steel and aluminum, in which the stainless steel forms the food contacting surface, also comes to mind but this would have the drawback of warping during use due to the differences in thermal expansion properties of the two materials when bonded in a bimetal construction.
A three-ply composite of stainless steel—aluminum—stainless steel also comes to mind for solving the thermal warpage problem, but this, too, is problematic because the stainless steel underside offers poor thermal responsiveness for the heater and thermostat.